Electrooptical system



Feb. 5, 1935. F. GRAY 1,990,183

ELECTROOPTICAL SYSTEM Filed June 25, 1951 Wmvm/e F694) Web Z177 URNE YPatented Feb. 5, 1935 UNITED STATES PATENT oFFIcE ELECTROOPTICAL SYSTEMFrank Gray New York, N. Y assignor' to Bell Telephone Laboratories,Incorporated, New York," N.-Y., a. corporation of New York ApplicationJune 25 1931, Serial Nations!) 12 Claims. (01. 178-6) "This inventionrelates toelectroroptical systems beam cannot be great. This arrangementis and more particularly to apparatus for producing therefore opticallyinefficient. P a beam'of light for spotillumination. s V "The otherarrangement in which the original It is now well recognizedthatthe,method of focus; of the beam is at the field ofview necessi- ;:,5illuminating a-subject or: object to bescanned for tatesztheintercepting of the beam by the re- '5 the transmission of a televisionimage which com- :flecting surfaces at a point where the beam has prisesilluminating the object by means of a considerable cross-sectional area.Since-the entravelingbeam of light has marked advantages tire:field ofview is swept over bythe reflected .over sorcalled flood lighting. j:beam while the reflecting surface is moving The usual apparatus forproducing the moving througha very small angle, the time takenbysthe 1 0beam of light is a rotating'disc provided with a reflecting surface tocompletely enter the beam spiral of apertures through which parallel orand then to completely leave the beam is aconsubstantially parallel raysobtained from an arc siderable portion of the time taken to sweep a lampare projected and moved across a large vbeamacross afield, that is,aline scanning period,

15 .lenswhich results in the rays being given a high since thereflecting element must be at least large 15 velocity ofmovementacross-the object, compared enough to receive; the entire lightfrom the beam. with the -,,velocity ofythe apertures. Light from Asamatter of fact it is advantageous to have the .the object-then impingesdirectly upon large stareflecting elements contiguous at the edges. The:tionary photoelectric cells or large optical collectperiodduring whicha reflecting surface is entert "2,0 ,ing surfaces ,which focus'the lightupon small ing or leaving the'beam might under these ,con-

photoelectric cells. v ditions be,,for example, a fourth oftheline-scan- I .Such. a system has the disadvantage that; the ning period.1 The same situation would be present 'lightsfrom the arcisnotveryaefficiently utilized. in a lensed disc arrangement if thelenseswere :At ,mostonly asmall amount of light can pass contiguous-attheedges and the stationary light '25 through each of the smallapertures in'the scanbeam were made narrow enough so that only two'ning. disc. It? has alreadybeen-proposed to sublenses, for, example,were simultaneously illumi- :.sititute.,large lenses for the smallapertures-of the -nated.. During thetime that the mirror or lensscanning'disc and illuminate this lensed-:discdlis entering; the beamandagain during the time ,rectly, from a point sourceof light. Such an ar-,that it is leaving the beam. the light could ob rangement .is-muchmore. efficient than that em- .viouslynotbe utilized for scanning. Thiswould v3 ploying a disc withsmallapertures. l lensed result in a verymaterial loss of 'lineor trans-p disc however has the disadvantagesthat;good missiontime; lenses are expensive and the-,weight of the disc isAnother object; of the present invention is to :such as .to introducelarge centrifugal forces. provide. a;system;for producing spotillumination .35 Plane mirrors on the otherhand are relatively of a feld ofview utilizing mirrors or lenses with inexpensive,,.andof smallermass. i a, concentrated beam of incident'light such a Oneof the objects.of the present invention is manner as to avoid the abOVB mentioned Wasteto provide .a rotating mirror arrangement for of nsm o i spotillumination Ora field of view which will I 1 0 d fi of the mventlonherein 40 have an Optical emciemy. of the Order. f that chosen forillustration and later'described indeno tail lightfrom a point source isassociated with a onverging lens or lens system to produce .a narrowconverging concentrated beam of light into the path of whichissuccessively movedre- 4 g i g angles m f tum -flectingsurfaces'circularly arranged upon a rox 1 Y x 1 0 m d tatable disc and havingprogressively. different wlthia'ipomtihghtsource/and stitlmlary anglesof inclination to the disc. All of these vergmg j' The beam, f focus-Sadangles of inclination are of the order of 45. The upon InlIIOIS 01' at0f VleW. C118 come to a at of lensed discs. I I

It has heretofore been'suggested to use a rotating elementprovidedwithplane mirrors set at .50 ea is focussed uponitheimirrors hreflected field of view and sweep thereacross in parallel m l htWi11'bfi p ly v u t horizontal lines. The light reflected from. theincidentbeam diverges rapidly, as is necessary objects within the-;field isreceived upon large if an intensebeamis tobeobtainedtfrom thephotoelectric cellsto set up the image currents. point source of light;but, sinceythe ispjotiof;light .To avoid the, above mentioned loss oftransmis on thefieldmustbe small; the-.diYerJ mcepflthe ;S,ion time asimilarsetof reflecting surfaces is 55 placedon the opposite side of thedisc in stagbeams supplied'by the mirrorsfi alternate with light source;and

ject 8.

rors 7.

gered relation with those of the first series and the anglesofinclination of the surfaces of the first series and the number ofthese surfaces are so chosen that the first series will scan alternatestrips of the entire field. The reflecting surfaces of the second seriesscan the intermediate lines, there being a second source of lightsimilar to the first cooperating with the second series of reflectingelements. Since the two stationary beams are aligned and thecross-sectional area of each beam is such as to illuminate at least halfof a reflecting surface when the surfaceis entirely within the path ofthe beam, a pair of staggered reflecting surfaces is simultaneouslyfully illuminated at each instant. While one of these sur faces issweeping its reflected beam acrossthe field the other surface isentering or leaving its incident beam. The field is of such size that asone beam completes its sweep the other is of normal intensity and readyto begin its sweep.

The optical efficiency of such a system as this can easily be made ofthe order of a thousand times that ofthe usual arrangement employing anapertureddiscr This-is obvious when it is appreciated that in theusualarrangement the light passing through a single aperture at eachinstant is 1/2500 of the total light of the illuminating beam in thecase where fifty apertures are employed, while in the system justdescribed the light of the entire beam from each source is utilized onehalf the time.

A more detailed descriptionof the invention follows and is illustratedin the attached drawing.

Fig. 1 illustrates a'television transmitting apparatus involving theinvention; 1 y Fig. 2 is a face view of the scanning Fig. 3 is an edgeview of aportion of the scann disc; I

Fig. 4 is a face view of a scanning disc having two sets of mirrorsco-operating witha single disc of Fig. 5 illustrates a portion of ascanning disc provided with two sets of lenses. a

' The television transmitter of Fig. 1 comprises 1 two sources of light1 and 2, lenses 3 and 4, a

'sion and a pair of light sensitive devices-9 shown,

by way of example, as photo-electric cells.

- Light from the source 1 'isconcentratedby the lens 3 into a beam whichis supplied to'th'e mirrors 6. The light beam is reflected by themirrors to effect spot illumination of the subject or field to betransmitted. 7

The mirrors 6 are angularly offset with respect to each other, so thatthe beam of light supplied by the successive mirrors illuminates orscans a different unit band or line of the subject 8.

In a similar manner light supplied by the source 2 is reflected by themirrors '7 which are offset withrespect to each other, so thatthe lightbeam supplied by the successive mirrors illuminates or scans "adifferent unit band or line of the sub- "Ihe unit bands or lines scannedby the light those illuminated by the beams from the mir- Thusduringjonerevolution of the disc 5 the subject will be completelyscanned in two alterrors 6 will produce a series of light beams whichlight beams which scan lines 2, 4, 6, etc.

Light reflected from elemental areas of the 7 subject 8, is applied tothe photo-electric cells 9.

beam, reflected by any mirror 6 of one row, leaves the right hand edgeof the subject 8, a mirror 7 of the other row is supplying a beam oflight of normal intensity to left hand edge of the field 8.

The advantage of the mode of operation described in the precedingparagraph will be apparent from the following considerations.

. Assume, for example, that, but one light source 1 and one row ofmirrors 6 are provided, that the mirrors are'so set with respect to eachother that they supply light beams respectively illuminating successiveunit bands of the subject 8 without a break in the continuity of theillumination, and that the subject 8 is completely scanned during onerotation of the disc 5.

If the light beam, into'whichthe mirrors are introduced and from whichthey are withdrawn, were infinitely small, that is, without dimensions;it would be possible to introduce and withdraw the mirrors withoutcausing variations in the intensity of the light supplied to the subject8. However, since thebeam supplied by the source 1 has finitedimensions, the'inten'sity of the light supplied to the subject willvary duringdefinite intervals of time for each-mirror.

As the mirror enters the beam, the intensity of the light applied to thesubject will increase from a-low va1ue,-as the advancing edge of themirror begins to enter the beam, to a normal value when the mirror iscompletely within the beam. Conversely,-as the mirror leaves the beam,the intensity of the light applied to the subject will vary from anormal value to a low value as the trailing edge of the mirror passesoutof the beam. Since this occurs for each mirror, the tone values of Ielemental areas along the two edges of the image produced at thereceiving station will differ, from the corresponding elementalareas ofthe subject scanned at the transmitter, by amounts determined by theposition of the mirror with respect to the beam.

The above noted-condition may be avoided,lby'

so adjusting the mirrors with respect to the beam from the source that ascanning beam is only applied to the subject during the time when thelightisupplied by the mirrors is of normalintensity. This isobjectionable forthe reasonthatif the width of the field isnotreducedthetimev rehence during these intervals the transmission circult isidle. I V

In' either case there are definite intervals'of time when the line'lsnot used and hence the unetime operating efiiciency of the systemisreduced. Fig. l-illustrates an alternative scanning mech anism whichmaybe used in the system hereinbefore-described 'This mechanismcomprises a rothe mirrorscot-each seriesilliI andili,zrespectivelygz Isupply-photo-electric currents to thegztransmis of adjacent elements of8,011;,IQWi 'bBiHgILQffQbh tarydisc-l2 carrying two IOWSLOfI mirrors 13randseelementsein :pathsrintersecting said. rays, ioneisei-i 1 14, whichco-operate with a.beamrofilightsupplied: through the lens 11.Asinthewpreviously; xdescribedszsoaiiniirigmnit,

are ofiset with respectato eachcothenandrare:sup plied with, lightfromtheisourceithrough lensalito produce two beams;of:,light;whichcaltemately illuminate successive bands: or linesrofthe-la field or area to be transmitted. Againcthetseriesel riesintersecting;cone:portion of; said :rayszwhiles' thegtotherzr intersectsa ,dififerent portion: thereof;

and-meansrfor imaintaimngethe .differentelements f ofjeaGhfQfFSaidfJI'OXVSE during- .theinmovement gin; 5 positicmfor causingitheselementsiof :each rowzrto move theircmerging;beams: in vsuccessionacross respective elementali-strips ofsaid field :in alter-:1 nation,wit-lr.correspondingelements:of thegother;

of saida3rows theudimension10f, the path; of said;

ofmirrors 13 are staggered;with;;respe.ct :to ztheo:istationarylightrays in thedirection of movements series 14 so that,they co-operate;to maintain'continuity in the illumination suppliedtoxthe:elemen of msaid Jelements being such {at areflecting, ,surfacethat: the incident lightv extends, a consider:

the illumination is always ,of. =;normal;intensity. ,1,

but": does not: simultaneously' cover two adjacent; 15

The. principles of this inventicn'may: be applied elements; 1:

to a scanning mechanism 'includinggxcondensing7L:

lel; elementalstr-ips comprising; means. for settin'grr I to each other.,Ihesehalf-lensesare:arrangedzona;v

each side of the circle,ythatr-is -on a line :paralleh totheperiphery ofthe "disc.

As in the mirror system-:of.- Fig.:4, the lenses-1: supply light beamswhichp-scan alternatenumt bands. of thesubjectand each lens iscompletelywithin the path of the, lightifromrthe'sourcetl5, before the scanning,beamisapplied tothe area; to be scanned.- Again, because ofthe-staggered... effect, the two rows of lenses .co-opemteto. supply; :2

3.;.Meansifor.scanning.a field. of .yiew in parala up stationary lightrays, two similar rows of lightw;

directingielements; thev distance between'centers 20 riesintersectingaone. portion of :saidv rays .while 25 the, other intersectsa different portion thereof; and vmeans for maintaining, thedifferentieleew' mentslofu-each of said rows. durmgptheir-j,:move-,= ment inposition forcausing the elementsof each row-v to movev theiremergingtbeams-in succession 30 across respective elemental strips of'saidfield alternation; with ;corresponding ,1elements of the, other ofsaid rows with .avelocityrgreater at said; 3 i

an illuminating'beam of normal lightrintensityrto :field than-thevelocity of said light directing elesion circuit: 1 1 i Consequently theimage currents supplied tor.-

the transmissioncircuit; correspondsto theeactua tone values of thefield scanned: and-theiline tim emciency'of the system-is notireducedwt"What is claimed is:

1;. Means for scanmng a field of iviewzin paral -J lel elemental stripscomprising meansrfonsettin up stationary light rays twosimilarcrowszofcligh directing elements, the distance; between: centeorder of the dimension of; each; element :alon line joining theircenters;meansfor'moyingisai elements in paths intersecting ;-sai d;rays., .:one.; series intersecting one po-rtion-,of;said rayscwh-il theother intersects a different portion thereof-m;

andJmeans "for maintaining the different elements of each of said rowsduring their movement in position for causing the elements of each rowto move their emerging beams in succession across respective elementalstrips of said field in alternation with corresponding elements of theother of said rows.

2. Means for scanning a field of view in parallel elemental stripscomprising means for setting up stationary light rays, two similar rowsof light directing elements, the distance between centers of adjacentelements of each row being of the order of the dimension of each elementalong a line joining their centers, means for moving said ments. a

4. Means for scanning, a field of view of parallel elementalstripsicomprising-means for setting upystationary light,rays-,-twosimilar seriesiof circularly; arranged reflecting elements, ;the'distance between centers :ofva'djacent elements: of each i 4riesbeing-cf the order of the dimensionpi each-: elementg alonggthe linejoining, their; centers, means.;-;for moving said .elements in -paths,inter ectingq'said; rays,- ione-series intersecting-ona pore tion;; of.said rays Awhile the other intersects a 45 difierenttportionrthereotand me'ans1iQ ;-'main-- taining :the different elements of each of ,saidse iesuduring; their moyement in -position for. caus-m elemcntalqstripsof, said ,field in alternation gwithw corresponding elements ofthe;othersof ysaidvseei 165;": i 1n f,

5 ,Means f, or scanning a field of iew of -paralupxstati'onary a-lighti::r'ays, two.v similar; series .=of ,3, circularly: Sarranged reflectingelements; theidi tance between i centers of adjacent elements :of i

each-series being of the'order of the dimension of each element alongthe line j oining their 'centera means for moying -said elements paths 7inter-'- secting said rays;*one series intersecting oneportion of saidrays while the otherintersects a different portion thereof, and meansfor maintaining the different elements of each of said se- 5 ries duringtheir movement in position for causing the'elements of'each seriestomove their emerging beams in succession across respective elementalstrips of said field in alternation with 70 7 corresponding elements ofthe other of said series', the dimension of the path of said stationarylight rays in the direction of movement of said elements being such at areflecting surface that the incident light extends a considerableportion el,. ele-mentalstripscomprising,;,means forwsettings at leastofthe width of the elements, but does not simultaneously cover twoadjacent elements.

6. Means for scanning afield of view in' parallel elemental stripscomprising means for setting up convergent light rays, two similar rowsof light directing elements, the distance between centers of adjacentelements of each row being of the order of thedimension of each elementalong a line joining their'centers, means for moving said ;-elements inpaths intersecting said rays,'one series intersecting one portion ofsaid rays while the otherxintersects a difierent portion thereof, and

meansfor maintaining'the different elements of eachof said rows duringtheir movement in position for causing the elements of each row to movetheir emergingbeams in succession across respecorder of thedimension ofeach lens along the line joining their centers, means for moving saidlenses in paths intersecting said rays, one series intersecting oneportion of said rays while the other intersects a differentiportionthereof,'and means for maintaining the different lenses of each ofsaidseries during their movement in po-' sition for causing the lensesof eachseries to move their emerging beams across said field inalternation with corresponding lenses of the other of said series.

8. Means for'scanning a field of view in parallel elemental stripscomprising means for setting up stationary non-contiguous light beams,two similar series of light directing elements; the distance betweencenters of"adjacentelementsin each series being of the order of thedimension of each element alonga line joining their"cen-' ters, meansfor moving said element'sin paths intersecting said rays, one seriesintersecting one of said beams while the other intersects the other ofsaid beams, and means for maintaining-the different elements of each'ofsaid rows during their movement in position forcausing-the ele-" mentsof each row to move their emerging beams 50 in succession acrossrespective elemental strips of said field in alternation withcorresponding elements of the' otherof said rows. 9. Means for scanninga field of view in parallel elemental strips comprising "means for set-1ting up stationary light rays, two similar series of light directingelements; the distance between centers of adjacent elementsin eachseries being of the order of the dimension of eachelement' along a linejoining their centers and the elements of one series being staggeredwith respect to those of'the other, and means for moving said elementsin paths intersecting said rays to cause v elements of each seriesalternately tomove their emerging beams in succession acrossrespectivestrips of said field.

10. Means for scanning a field of view in paral- 1 lel elemental stripscomprising means for setting up light rays,'two similar rows of lightdirecting elements, the distance between'centers of adjacent elementsofeach row being of the order of other intersects a 'd'iflerent portionthereof, and

means for maintaining the different elements of each of saidrowsduring'their movement -in po sition for causing theelements' ofveachrow to 'theidimension of each elementalong a line join- F ing theircenters, means for moving said 'ele-j ments in paths intersecting saidrays; one series intersectingone portion of said rays while the movetheir emerging beams in succession across respective elementalstri'psoi? said field in alternation with corresponding elements of theother of said rows. I 11. Means for scanning a field of view in parallelelemental strips comprising means forproducing two light beams; twolight directing ele-j,

ments, means for producinguniform relative motion between one beamand-one element ina direction transverse of said bea'm and simulta- Ineously the same relative motion between' the other of said-beams andthe otherof said elements to cause said elements andtheir beams .to v Ibeams which respectively scan different strips of elemental width ofsaid-field so thatasthe area intercept each other and thereby formemerging of interceptibniof one element becomes a maximum thaton theotherelement begins to decrease, the dimensions in'said directions bothof said beams and or said elements being sogreat that thedistancecovered by each scanning beam in the region of said-field duringthe completing of each said interception'ismany'times said elementalstrip width. H v t 7 12."Means for scanninga fieldof view inparallel'eleme'ntal strips comprising means for produc,- ingtwostationary'light beams, pairs of light directing elements, -means"forcyclically" moving said elements of each of said pairs in pathstransverse respectively to the axes of said beams to.

cause 'said elements and their respective beams to intercept each otherand form beams which emerge from said elements and respectivelyscanvdifierent strips of elemental width of said field; the elements of eachof saidpairs'being in such position relative to each other and theirrespective beams'that as thenarea of interception on one element becomesa maximum that on the" other elem'ent begins to decrease; thedimensions. jof said beamsand of said elements in a 'directiontransverse to said beams being so great that the distancecovered by eachscanning beam i'nthe region of the field during the completing ofeachinterception is many times "saidelemental strip width.

- 1 'FRANK GRAY.

